Welding on cars - what to disconnect

[reb78]

I have a few motors with ecu's and more electronics than I would like these days. When welding on a car, what of anything should I disconnect? I always tended to pull the cable out of the back of the alternator and disconnect the battery and main ecu but cars seem to have more ecus than I can get to these days!

What should i be doing? Is it sufficient to just place the earth close to the repair point?

 

[skotl]

I think this is one of these topics where 1,000 different people have 1,000 different opinions.
But I'll step in as the first

I don't think you need to disconnect anything. In fact, disconnecting the battery -ve might cause more harm because it removes a common ground for all of the components.
There is a common belief that you should have the welder return (earth) cable as close to what you're welding as practical - I'm not sure that the electrically this would make any difference, but it can't hurt.

 

[AKN]

There is a common belief that you should have the welder return (earth) cable as close to what you're welding as practical - I'm not sure that the electrically this would make any difference, but it can't hurt.

In my first job I was involved in a project looking at the radio emissions from arc welding processes we put together recommendations for minimising them. This was one of the key points together with keeping both welding cables together as much as possible to keep the loop area they form as small as possible. In terms of the effects on the car keeping the return clamp as close to the weld as you can with a really good, clean, connection means the welding current will take the easiest route back to the power source. Check for any panel joints, and eliminate them, in the current path which could divert the return current.
A long welding current return path through the car body will result in a significant voltage differential across it when welding, any vehicle systems with ground connections to the body spaced along the return path will have this voltage injected into them.

 

[zzr1200]

It can make a huge difference because the current is taking the shortest path to the earth and not earthing through electronic components

I use a surge protector across the battery terminals and to date no problems.

Same here, I've never had a problem, I don't even disconnect the battery, I use a surge protector and have the welding return connected very close to the welding area.

Some of the plant/vehicles that I have welded, when asking the manufacturers about welding repairs, state that ecu's must not be disconnected and lets face it, vehicles have so many ecu's these days that trying to find them is almost impossible.

 

[ajlelectronics]

Disconnecting the battery just turns a low impedance system into a high impedance one with aerials! If you absolutely insist on disconnecting the battery, at least tie the cables together electrically. However, disconnecting anything is pointless and a waste of time.

"Surge protectors" are a useless placebo that merely lighten the wallet, rather than achieve anything useful. The battery is going to offer the lowest impedance regardless.
Now wait for all the posts where the headlights failed after welding the body etc!

 

[premmington]

Disconnecting the battery just turns a low impedance system into a high impedance one with aerials! If you absolutely insist on disconnecting the battery, at least tie the cables together electrically. However, disconnecting anything is pointless and a waste of time.

"Surge protectors" are a useless placebo that merely lighten the wallet, rather than achieve anything useful. The battery is going to offer the lowest impedance regardless.
Now wait for all the posts where the headlights failed after welding the body etc!

I am with you on the above - leave the battery on!

 

[zzr1200]

"Surge protectors" are a useless placebo that merely lighten the wallet, rather than achieve anything useful. The battery is going to offer the lowest impedance regardless.

There have been times when I've forgotten to use a surge protector and not had any problems, so maybe they are a waste of money, but its peace of mind for me......

 

[ajlelectronics]

There have been times when I've forgotten to use a surge protector and not problems, so maybe they are a waste of money, but its peace of mind for me......

Have a look inside one!

 

[Morris]

I would worry more about the risk of setting fire to the car.
Ask me how I know...

 

[zzr1200]

I would worry more about the risk of setting fire to the car.
Ask me how I know...

Been there got the T Shirt.....


PS. Well almost....

 

[sg66]

As first post, if its something silly expensive I remove ecu, keep battery on keep clamp lead as close to welding point as can, never had a prob yet.

With stick thou had one problem, luckily it was an on site freebie for an Irish fella called Johnny 6 fingers.

Stick this bracket back on me truck man, no, I might break truck, I just didn't want to do it, be fine, no, be fine, no, take battery and ecu off, no just do it, so I did,, he was still there 2hrs later as I left site with a cab that wouldn't start, I gave a nice big wave as I left.

 

[The_Yellow_Ardvark]

I allways leave battery connected, I had a surge protector, ( now with a friend). Return clamp as close as posible.

Never had an issue.
I have heard the horror stories of frien ECU's, mostly on the WWW.

 

[Burdekin]

Fit the earth close to where you are welding and you will be fine..

 

[m_c]

Any "welding destroyed my alternator/ECU" type posts I've seen that actually told the truth, generally involved somebody doing some thing stupid, like attaching the welder earth lead to the battery earth.
I also remember one tale about somebody who seized an engine after welding a crank pulley on. They earthed to the engine block, and it turned out it welded a main bearing shell to the crank.


Personally, battery gets left connected. Earth lead as near the weld as practical.
If you do have a surge protector, use it, but most modern ECUs are well protected for transients voltages, and the battery helps absorb them as well.

 

[Myles1970]

Have a look inside one!

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[tom2207]

Have a look inside one!

id love to see whats in one just out of curiosity

 

[tom2207]

ive welded on things for a long time , sometimes I take the battery off , sometimes I dont , it never seems to matter Ive never had anything fail after welding. but these days Im wary of taking a battery off anything unless theres a computer and all the software to hand to put things right again . Ive seen range rovers with flat batteries and they simply wouldnt start again without a bit of help , so if that was something exotic and it wouldnt start it could be a major headache , long gone are the days of bump starting things.

 

[doubleboost]

The battery acts as a surge protector
Been welding cars all my life never had a problem
I normally weld a tab on to the body work for the earth

 

[grim_d]

No need to do anything other than put the return lead as close as physically possible to where you are welding.

Because science.

 

[pedrobedro]

Any "welding destroyed my alternator/ECU" type posts I've seen that actually told the truth, generally involved somebody doing some thing stupid, like attaching the welder earth lead to the battery earth.
I also remember one tale about somebody who seized an engine after welding a crank pulley on. They earthed to the engine block, and it turned out it welded a main bearing shell to the crank.


Personally, battery gets left connected. Earth lead as near the weld as practical.
If you do have a surge protector, use it, but most modern ECUs are well protected for transients voltages, and the battery helps absorb them as well.

I welded a Toyota Hi Ace crank pulley on and it's still running now. It was a bodge for a mate and it's done quite a few miles since then. I remove the ground cable usually but sometimes forget. I remember a lad I worked with years ago stick welding a Mini boot floor and he burst his battery when he got a sticker.